President Trump’s cabinet of department secretaries and advisors lurches from tweeted firings to unprecedented numbers of new appointments.

Former Secretary of State Rex Tillerson, a good man humiliated for trying to do his job, is only one of many caught in the flood of incoming and outgoing.

The State Department he headed is one of the original three U.S. government departments begun under George Washington.

The purpose of more recently created departments may be a bit fuzzy, but the purpose of the State Department is clear and always has been. The State Department’s purpose is to handle U.S. relations with other countries.

The State Department’s Foreign Service Officers, otherwise known as diplomats, train to carry out their mission to the rest of the world, like members of the military for their assignments.

They learn foreign languages, study the history and culture of the countries where they will serve, and train for managing outposts of the U.S. in foreign countries. On average, they spend two-thirds of their careers in those countries.

Their duty is to use their skills and on-the-ground experience to serve the various presidents and their administrations. “Serve” is the operative word.

Yet presidents sometimes disdain their diplomatic servants. Roger Grant Harrison (“Will the State Department Rise Under Pompeo?” American Interest, April 4, 2018) suggests why this might be so.

Wrote Harrison: “The problem with career Foreign Service Officers is that they know too much. They know why your simple-minded plan to invade Iraq and install a democracy won’t work. They understand the tribal, ethnic, and familial loyalties that will frustrate your efforts to consolidate the opposition to the Assad regime in Syria, and why the endlessly trained Afghan military will never win the victory that American generals endlessly promise.”

Ah, well, they try. And will try again, under Mike Pompeo or whoever finally takes over from Rex Tillerson.